The present invention relates to an input and/or output unit of a scanning type. In particular, the invention relates to a beam scanning device for an input and/or output unit for a picture which is constituted in such a way that the sampling position of picture elements in the main scanning direction thereof is constant.
There has previously been employed a scanner in the conventional input and/or output unit of a beam scanning device. It is well known that the speed of a spot of light outputted by the scanner at the circumference on the scanned paper surface is higher that at the center.
Thus, as shown in FIG. 1(a), the amount of overlap of spots for adjacent sampling periods is low at the edges of the paper, while the amount of overlap is high at the center of the paper. Hence, the sampling density is low at the edges of the paper while the sampling density is high at the center of the paper in the conventional scanning type input and/or output unit. Thus the conventional unit suffers from a drawback in that the linearity of the sampling position of the picture element in the main scanning is not good.